The invention relates to the field of operational amplifiers, and in particular to a circuit that prevents load-induced DC non-linearity in an op-amp.
An operational amplifier is a AC or DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. In its ordinary usage, the output of the op-amp is controlled by negative feedback which, because of the amplifier's high gain, almost completely determines the output voltage for any given input.
Op-amps are among the most widely used electronic devices today, being utilized in a vast array of consumer, industrial and scientific devices. General-purpose integrated op-amps of standard specification are inexpensive. Modern designs are electronically more rugged than earlier implementations and some can sustain direct short-circuits on their outputs without damage.
The operational amplifier was originally designed to perform mathematical operations by using voltage as an analogue of another quantity. This is the basis of the analog computer where op-amps were used to model the basic mathematical operations (addition, subtraction, integration, differentiation, and so on). However, an ideal operational amplifier is an extremely versatile circuit element, with a great many applications beyond mathematical operations. Practical op-amps, based on transistors, tubes, or other amplifying components and implemented as discrete or integrated circuits, are good approximations to the ideal.
However, once an op-amp includes a load, distortion usually results. One of the ways to accommodate this problem was to provide more current gain to the op-amp. This over time made the op-amp unstable and unpredictable.